Long-term repeatability of exhaled breath condensate pH in asthma.

Exhaled breath condensate (EBC) is being used increasingly to sample airway fluid. EBC pH may be a biomarker of airway inflammation in asthma. In this study, we assessed the long-term reproducibility of EBC pH in asthma. We examined 31 asthmatic patients and eight healthy subjects three times over a 1-year period (winter, autumn and summer). EBC pH was measured after argon deaeration. Repeatability of pH measurements was assessed using intraclass correlation coefficients (ICC) and the limits of agreement (LOA) between seasons were calculated according to Bland-Altman method. No significant differences in EBC pH between seasons were detected in healthy subjects and asthmatic patients. EBC pH showed high repeatability either in healthy subjects (ICC=0.94) or in asthmatics (ICC=0.97). Variability between seasons was greater in asthmatics than in healthy subjects: winter-autumn LOA -0.68/+0.52 and -0.31/+0.31, autumn-summer LOA -0.75/+0.67 and -0.24/+0.15, winter-summer LOA -0.92/+0.67 and -0.34/+0.23 in asthmatic and healthy subjects, respectively. In a subgroup of 11 asthmatics who remained in stable conditions during the study, no substantially different LOA were observed in EBC pH compared with the whole group of asthmatics. Asthmatic smokers (n=10) tended to have lower EBC pH (7.57+/-0.46) than asthmatic non-smokers (n=21) (7.74+/-0.21; p=0.063) and wider LOA. In conclusion, we demonstrated that EBC pH exhibits good repeatability in long-term assessment. EBC pH in asthmatics tended to fluctuate more than in healthy subjects. However, EBC pH variability in asthma was not influenced by changes in clinical status. Rather, we suggest that cigarette smoke may be implicated in EBC pH variability.

Measurement of exhaled nitric oxide in healthy adults.

BACKGROUND AND AIM: Measurement of exhaled nitric oxide (NO) is useful in the diagnosis and management of asthma. The aims of this study were to investigate the effects of physiologic confounders on levels of fractional exhaled NO (FE(NO)) in healthy adults and to establish reference values of FE(NO) measured according to American Thoracic Society (ATS) guidelines. METHODS: FE(NO) was measured in 122 healthy nonsmoking subjects of 20 to 65 years with a chemiluminescence analyser using the single breath online technique and an exhalation flow of 50 mL/s. RESULTS: The geometric mean [SE] FE(NO) was 21.6[1.06] ppb in males and 16.3[1.07] ppb in females (p < 0.01). FE(NO) increased significantly with body size and spirometric indices. In a stepwise regression analysis, body weight was the only variable included in the model (r = 0.36, p < 0.0001) and explained gender differences in FE(NO). When weight-related variables, including BMI, BSA and dead space volume, were analysed in a stepwise regression model, dead space volume gave the best correlation with FE(NO) (R = 0.39; p < 0.0001). CONCLUSION: The present study estimated that mean FE(NO) in healthy Caucasian subjects of 20 to 65 years, measured according to ATS guidelines with the online single breath technique, ranges from 15 to 24 ppb depending on the body weight. We suggest that the volume of dead space may explain the effect of weight on exhaled NO. However, a substantial part of FE(NO) variability in normal subjects remains unexplained.